The first wave of globalization (1830-1914) witnessed a decline in the number of countries from 125 to 54. Political consolidation was often achieved through war and conquest. The second wave of globalization (1950-present) has led instead to an increase in the number of countries to a record high of more than 190. Political fragmentation has been accompanied by the creation of peaceful structures of supranational governance. This paper develops a theoretical model of the interaction between globalization and political structure that accounts for these trends and their reversal. We show that political structure adapts to steadily expanding trade opportunities in a non-monotonic way. Borders hamper trade. In its early stages, the political r...